It is not permissible to perform dangerous actions on machines/installations in a safety-relevant environment from any location. Controlling said installations was possible until now only at stationary points or using wired devices. However, these limiting factors have been removed as a result of wireless transmission technologies. In order to fulfill safety engineering requirements, zones must be technically defined and a unique assignment to said zones must take place. It is already known to define corresponding effective ranges within which a machine can be controlled wirelessly by means of a control device. In such cases the effective ranges are delimited by one or more RFID (Radio Frequency IDentification) transponders. High requirements in terms of safety are imposed on the use of such control devices in connection with the function of the effective ranges.
In order to be able to read or evaluate the RFID transponders, line-of-sight contact is usually necessary between the control device and the RFID transponder. In many cases, e.g. in large machines into which the user climbs, it is not possible or, as the case may be, necessary to cover the entire safety-relevant effective range with corresponding RFID transponders. For example, the safety-relevant effective ranges can be circumscribed by means of fences.